This invention relates to ignition systems for internal combustion engines, and more in particular to an apparatus for increasing the ignition voltage of internal combustion engines in motor vehicles.
It is known that combustion in the operation of motor vehicle internal combustion engines has hitherto only been incomplete, and hence that some of the fuel (generally 15 to 25%) is discharged unburnt together with the exhaust gases. One of the main reasons for this problem is the imperfection of the ignition systems currently in use.
In order to ignite a mixture of fuel and air, the ignition spark must have a given minimum energy, i.e. ignition energy. If the energy is less than this ignition energy then, although, a spark may occur, there will be no ignition of the gases. When they are in perfect condition, normal coil ignition systems produce adequate secondary voltage on the secondary side to ignite the gases, but the voltage induced in the secondary winding rises with increases in the primary current at the moment of opening of the contact-breaker contact. Since the primary current does not increase abruptly on closing of the contact, but rises with some delay to a steady current determined by the battery voltage and the ohmic resistance of the circuit, the maximum secondary voltage corresponding to the steady current is therefore attained only at low engine speeds or low spark frequencies. The time the contacts are closed decreases as the engine speed increases, so that there is reduced energy storage in the magnetic field of the ignition coil and hence a reduced secondary voltage at higher engine speeds. Thus, as the engine speeds increase, the energy of an increasing number of sparks may be inadequate to ignite the fuel-air mixture.
Apart from too short a closing time, reduced ignition voltage may result from leakages in the ignition circuit, for example due to leaking water, dirt and oily deposits on insulated parts, and combustion residues on the insulator foot of the spark plug. The same applies to the capacitative load. For example, a capacitative load may increase to such an extent due to dirt in the ignition system, and particularly the ignition lead, that the secondary voltage alone drops to half of the value that it would otherwise have. As soon as the condition of the ignition system departs from the ideal state, and in practice this is the case after just a short period of use, times during which ignition fails to occur become increasingly more frequent, particularly at higher engine speeds, owing to inadequate energy at the spark plugs. Particular difficulties arise in this respect upon starting of a cold engine, and if the battery is not fully charged.
Various ignition systems have been developed to solve the problem of inadequate ignition voltage. In one of these known ignition systems, a device of the above described type is used in which the ignition voltage is increased by means of a capacitor. The disadvantage of this known device is that it results in greater power consumption, it has low efficiency, and the circuit is complex and expensive. In addition, the difficulties are even greater when the known device employing a capacitor operates at high voltages and with high current.